My trouble is I would need loads more tanks to keep Malawis in as the amount of stunning fish available continues to grow and I want them all! So far my wife has one her stance of "it's either me or another tank" but who knows about the future

I've got the exact same problem. I got really lucky when my wife gave me the ok to build a rack in one of the hallways. I can squeeze in one more 3fter though, it's just finding more silent air pumps. I had a 6 way hailea running and that was to much. Currently on a 4 way hailea and internal filter for the juvies. But the airpump is still to loud especially on a night when kids are in bed. Can't go internal for the fry because they'll get sucked in. Was thinking the tetra maybe? Any tips?

I use eheim (inset in a sponge housing I bought) with sponge filters, hoover the tanks daily and do regular water changes. The noise is perfectly acceptable but there are only small tanks.i also run a eheim on the main tank and the pump itself is very quiet - it's the water bubbles noise that causes me the issue.